Does a washer-disinfector sterilize instruments?

No. A washer-disinfector cleans and thermally disinfects instruments, but the load is not sterile when the cycle ends. Instruments leaving the washer-disinfector still need inspection, assembly, packaging, and a full sterilization cycle.

What are the five stages of a washer-disinfector cycle?

Cold pre-rinse, wash with detergent, rinse, thermal rinse for disinfection, and drying. The cold pre-rinse comes first because hot water coagulates protein and bakes blood onto instrument surfaces.

Why does the pre-rinse use cold water instead of hot water?

Heat above about 140 degrees Fahrenheit coagulates protein, which seals blood and tissue onto the instrument. A cold pre-rinse flushes gross soil away while it is still soft and removable.

What is A0 on a washer-disinfector?

A0 is a number that expresses how much thermal disinfection a cycle delivered, based on the temperature and the time held at that temperature. Hotter and longer means a higher A0 and more microbial kill. It describes disinfection, not sterilization.

How should hinged instruments be loaded in a washer-disinfector?

Fully open. Spray arms and detergent cannot reach the box locks and serrations of a closed hinged instrument. Cannulated items go on lumen racks with the connectors attached so water flushes through the channels.

What should a tech check on the washer-disinfector every day?

Spray arms spin freely and are not clogged, detergent cartridges have adequate levels, filters and strainers are clean, the correct cycle is selected for the load, and the previous cycle record shows the cycle completed within parameters.

Washer-Disinfector Stages and A0 Explained for the CRCST Exam

What a washer-disinfector actually does

A washer-disinfector is the decontamination area's workhorse. It mechanically cleans instruments with pressurized spray (impingement) and detergent, then thermally disinfects them with a high-temperature rinse. Cleaning plus disinfection, in one automated cycle.

The single most important fact about this machine: it does not sterilize. Instruments leave the washer-disinfector clean and disinfected, but they are not sterile. They still need inspection, assembly, packaging, and a full sterilization cycle before use on a patient. The exam tests this distinction relentlessly.

The five stages, in order

Cold pre-rinse Cold water flushes away gross soil, blood, and loose debris. Cold on purpose: hot water coagulates protein and bakes blood onto the instrument surface, making it harder to remove. Memory anchor: cold first, because hot water cooks the blood on.

Wash with detergent Heated water plus detergent, delivered through rotating spray arms that hit every surface (impingement). The chemistry and the spray action work together to remove soil the pre-rinse left behind. Memory anchor: detergent does the chemistry, spray arms do the elbows.

Rinse Clean water flushes out the detergent and the loosened soil. Detergent residue left on instruments can carry over into sterilization and interfere with steam contact, so this step matters. Memory anchor: rinse the soap, or the soap follows you into the sterilizer.

Thermal rinse (disinfection) A high-temperature water rinse that thermally disinfects the load. This is the stage that delivers the A0 value the exam asks about. Moist heat kills vegetative microorganisms, but it is disinfection, not sterilization. Memory anchor: the thermal rinse is where A0 lives.

Drying Heated air dries the instruments. They come out ready for the assembly area: dry, clean, and disinfected, but still requiring inspection, packaging, and sterilization. Memory anchor: dry enough to handle, not sterile enough to use.

A0: the disinfection number

A0 is the number that ties heat and time together to express how much thermal disinfection a cycle delivered. It accounts for both the temperature reached and how long it was held there. Hotter and longer means a higher A0, which means more microbial kill.

What A0 is not: a sterilization claim. A washer-disinfector cycle can have a strong A0 and still produce instruments that are not sterile. The exam loves the wording "the washer-disinfector achieved an A0 of X, so the instruments are sterile." That answer is always wrong.

Load it like you mean it

Hinged instruments go in fully open. Spray and detergent cannot reach box locks, serrations, or the inside of a closed hinge. Open every ratchet to the first click or fully open per the IFU.
Cannulated instruments connect to lumen racks. Attach the irrigation connectors so water flushes through the channels. A lumen that gets sprayed only on the outside is not cleaned.
Do not overcrowd or nest items. Shadowing, when one instrument blocks the spray from reaching another, leaves dirty spots that look clean.
Keep spray arms clear. Tall or hanging items that block the arms turn a wash cycle into a soak cycle. The arms must spin freely through the whole chamber.
Match the cycle to the load. Delicate instruments, plastics, and powered devices may need different cycles or hand cleaning per the IFU. When in doubt, the IFU wins every argument.

Daily checks and monitoring

Spray arms rotate freely and spray holes are not clogged with scale or debris.
Detergent cartridges have adequate levels and dosing is correct for the cycle selected.
Filters and strainers are clean, so recirculated water stays clean.
Water temperature readings and cycle printouts confirm each cycle ran within parameters.
Cycle records are kept. Documentation proves the cleaning and disinfection happened, which matters for traceability and for the exam.

Exam traps to dodge

Trap: "The washer-disinfector cycle finished, so the instruments are sterile." Wrong. Cleaned and disinfected, never sterile. They still go through inspection, assembly, packaging, and sterilization.

Trap: "The pre-rinse should use hot water for better cleaning." Wrong. Hot water coagulates protein. The pre-rinse is cold, always.

Trap: "A high A0 means the load is sterile." Wrong. A0 measures thermal disinfection. Sterility comes only from a validated sterilization process with monitoring.

Trap: "Closed hinged instruments are fine in the washer-disinfector." Wrong. Open them fully so the spray reaches every surface.

Trap: "Detergent choice does not matter as long as the cycle runs." Wrong. The wrong chemistry damages instruments (alkaline on aluminum, for example) and residue interferes with sterilization.

Washer-Disinfector: Stages, A0, and Exam Traps